The room temperature afterglow mechanism in carbon dots: Current state and further guidance perspective

Recently, researchers are no longer satisfied with the investigation of the fluorescence properties of carbon dots (CDs), but instead focus on the more attractive afterglow luminescence, especially room temperature phosphorescence (RTP) and thermal activation delayed fluorescence (TADF). Numerous attempts have been made to construct CD-based afterglow materials, including embed CDs in various rigid matrices or construct self-protective structures. Because of the diversity of construction methodologies, different mechanisms and effects would be produced, thus resulting in distinguishing afterglow characteristics. Afterglow of CDs in organic matrices is mainly due to the formation of hydrogen bonds, which can suppress intramolecular vibration and stabilize triplet states, thus generating afterglow emission. Afterglow of CDs in diverse inorganic matrices are completely different because the multifarious interactions between CDs and different matrices are generated (e.g., rigid structure covalent bonds, structural confinement, energy transform, etc). The self-protective CDs always possess polymer-like structure or polymer-chains on their surface, which can act as rigid matrix to activating afterglow emission. This review aims to sum up the relationships between structure construction and afterglow characteristics, and the mechanism of afterglow generation, which are of great significance for stimulating more exciting progress in the purposeful design of afterglow materials. (c) 2020 Elsevier Ltd. All rights reserved.